Chemical properties of titanium and titanium alloys

The titanium in a relatively high temperature, can be used with many elements and compounds react. Various elements can be divided into four categories, according to their different reactions occur with titanium:

First class: halogen and chalcogen and titanium is to generate the compound of the covalent bond and ionic bond;

Transition elements, hydrogen, beryllium, boron, carbon and nitrogen group elements with a titanium intermetallic compound is generated in the second category: and limited solid solution;

Class III: zirconium, hafnium, vanadium family and chromium family, scandium element with a titanium infinite solid solution is generated;

Fourth class: inert gas, alkali metal, alkaline earth metals, rare earth elements (except scandium outer), actinium, thorium, etc. does not occur with a titanium reaction or substantially does not react.

The reaction with the compound:

◇ HF and fluoride

Hydrogen fluoride gas when heated reacts with the titanium to generate TiF4, reaction of formula (1); the bifluoride liquid free of water may be generated in the titanium on the surface of the dense layer of titanium tetrafluoride film, prevents HF immersed in the inside of the titanium. Hydrofluoric acid is the strongest flux of titanium. Even a concentration of 1% hydrofluoric acid, can also occur with a titanium intense reaction, see formula (2); anhydrous fluoride and its aqueous solution at a low temperature does not react with titanium, melted at high temperatures only a fluoride significant reaction occurs with titanium.

Ti +4 HF = TiF4 +2 H2 +135.0 kcal (1)

2Ti +6 HF = 2TiF4 +3 H2 (2)

The ◇ HCl and chlorides
The hydrogen chloride gas can corrode the metal titanium, dry HCl> 300 ℃ reacts with titanium TiCl4, see equation (3); concentration <5% hydrochloric acid at room temperature without reaction with the titanium, 20% hydrochloric acid at room temperature with a titanium occurs melon generated purple the TiCl3, see formula (4); when the high temperature long, even if the dilute hydrochloric acid is also corrosion titanium. A variety of anhydrous chlorides, such as magnesium, manganese, iron, nickel, copper, zinc, mercury, tin, calcium, sodium, barium, and NH4 ion and its aqueous solution, are not react with the titanium, titanium chloride has good stability.

Ti +4 HCl = the kcal of TiCl4 +2 H2 +94.75 (3)

2Ti +6 HCl = TiCl3 +3 H2 (4)

◇ sulfuric acid and hydrogen sulfide
Titanium and <5% of diluted sulfuric acid after the reaction to generate a protective oxide film on the titanium surface, to protect the titanium is not dilute to corrosion. But> 5% sulfuric acid and titanium have significant reaction, and about 40% sulfuric acid at room temperature, the fastest speed of the corrosion of titanium corrosion slower speed but, when the concentration is greater than 40%, reaching 60%, 80% of another to achieve the fastest. The heated dilute acid or 50% sulfuric acid reacts with titanium sulfate, titanium see formula (5), (6), heated concentrated sulfuric acid can be reduced by titanium, generating of SO2, see formula (7). Room temperature the titanium reacts with hydrogen sulphide, generated in the surface thereof a layer of protective film, and can prevent the further reaction of the hydrogen sulfide and titanium. However, at high temperatures, the reaction of hydrogen sulfide and titanium precipitates hydrogen, the formula (8), sulfides of titanium powder titanium generated with the reaction of hydrogen sulfide started at 600 ℃ at 900 ℃ reaction product mainly as TiS, 1200 ° C for Ti2S3 .

Ti + H2SO4 = TiSO4 + H2 (5)

2Ti +3 H2SO4 = Ti2 (SO4) 3 + H2 (6)

2Ti +6 H2SO4 = Ti2 (SO4) 3 +3 SO2 +6 H2O +202 kcal (7)

Ti + H2S = TiS + H2 +70 kcal (8)

◇ nitric acid and aqua regia
Dense and smooth surface of the titanium nitrate has a good stability, which is due to nitric acid can be quickly generated in the titanium surface layer of a solid oxide film, but a rough surface, in particular titanium sponge powder or titanium, with times, hot dilute nitrate react, see formula (9), (10), higher than 70 ℃ concentrated nitric acid can also be with the titanium reaction, see formula (11); room temperature, the titanium reacted with aqua regia. The temperature is high, titanium with aqua regia reaction generated TiCl2.

3Ti +4 HNO3 +4 H2O = 3H4TiO4 +4 NO (9)

3Ti +4 HNO3 + H2O = 3H2TiO3 +4 NO (10)

Ti +8 HNO3 = Ti (NO3) 4 +4 NO2 +4 H2O (11)

To sum up, the nature and temperature of titanium and its existing form, purity has a very close relationship. The dense metal titanium nature is quite stable, powder titanium in the air can cause spontaneous combustion. The presence of impurities in the titanium, a significant effect of titanium physical and chemical properties, mechanical properties and corrosion resistance. Especially some interstitial impurities, they can make the titanium lattice distortion occurs, and affect the various properties of the titanium. The chemical activity of titanium in the room temperature is small, the reaction with hydrofluoric acid, etc. few substances, but the temperature is increased activity of titanium increased rapidly, especially at high temperatures, titanium and titanium alloys may react violently with many substances. Titanium smelting process are generally in a high temperature of 800 ° C or above, and must therefore be operation in a vacuum or in an inert atmosphere.